Communication system, communication device, and communication method

ABSTRACT

Respective nodes N 1  to N 3  only detect a carrier, and the node N 3  sets a random time between a time after a certain period of time t 1  and a time until a certain period of time t 2  after the carrier of data D 11  is gone as a waiting time so as to transmit data within this waiting time. The node N 2  transmits ACK data D 12  with respect to the data D 11  to the node N 1  before the certain period of time t 1  after the carrier of the data D 11  is gone. The node N 3  detects the carrier of the ACK data D 12  and again sets a random time after the certain period of time t 1  until the certain period of time t 2  to transmit the data.

This application is the national phase under 35 U.S.C. § 371 of PCTInternational Application No. PCT/JP01/04973 which has an Internationalfiling date of Jun. 12, 2001, which designated the United States ofAmerica.

TECHNICAL FIELD

The present invention relates to a communication system, a communicationdevice, and a communication method by which a plurality of communicationdevices connected to a transmission line adjust transmission timing ofdata based on a detection result of a carrier signal of anothercommunication device to prevent a collision between signals, whereby thedata can be efficiently transmitted/received.

BACKGROUND ART

In recent years, in order to reduce costs and effectively employexisting equipment without newly installing more communicationfacilities, a “power line modem” in which communication is performedutilizing an existing power line (also called an electric light line)has received attention. By networking electrical appliances, such as ofinside/outside houses, buildings, factories, and stores, connected by apower line, the power line modem can perform various processes such ascontrol of the appliances and data communication.

As a wired system digital communication other than networking of suchelectrical appliances, that is, a network communication that employs aplurality of power line modems which are multiply connected outsidehouses, Internet communication and the like employing a personalcomputer may be cited.

In a bus-type network such as the power line and the like, accesscontrol is performed, conventionally employing CSMA/CD (Carrier SenseMultiple Access/Collision Detection) system. In the CSMA/CD system, eachnode monitors a transmission medium such as a power line, confirms thatthere is no carrier on the transmission medium, and transmits a packetfrom itself node, and when detecting a collision, waits a certain periodof time to retry the transmission of the packet. A collision isdetected, for example, by a monitor electric power of the time of acollision is doubled, or a node itself receives data transmitted andconfirms whether the data corresponds to detect a collision.

Processing in which the CSMA/CD system is employed is explained. FIG. 8is explanatory views explaining the CSMA/CD system. FIG. 8( a) is adiagram illustrating a bus-type network in which three nodes NA to NCare connected to a transmission line NM, and FIG. 8( b) is a time chartillustrating access control by the CSMA/CD system. In FIG. 8, whentransmission requests are generated at time points TB, TC on the nodesNB, NC, respectively, while the node NA is sending out data DA, thenodes NB, NC are monitoring the carrier of the data DA on thetransmission line NN and perform access control to permit transmissionafter waiting times tB, tC which are decided by random numbers from thetime when the carrier of the data DA is gone. In this case, since thewaiting time tB is longer than the waiting time tC, data DC is sent outto the transmission line NN from the node NC prior to others. As result,the node NB detects a carrier on the transmission line NN once again,and awaiting time decided by random numbers is again set so that data issent out after this waiting time that is after the carrier of the dataDC is gone.

However, in a bus-type network which does not adopt the CSMA/CD systemdescribed above and is composed of a node detecting only a carrier on atransmission medium, a collision cannot be detected. Thus, when ACK datarepresenting a reception confirmation transmitted after a datatransmission from the node of a transmission destination collides, sinceretransmission of the transmission data is executed and the node of thetransmission destination doubly receives the same transmission data,there is a problem that the transmission efficiency deteriorates.

That is, when a collision can be detected, since the collision of theACK data can be detected, only retransmission of the ACK data may beperformed. However, when the collision of the ACK data cannot bedetected, it is determined that the transmission data has not beennormally received based on the phenomenon that the node of thetransmission destination has not received the ACK data within apredetermined time period, and the transmission data is retransmitted sothat the transmission destination node performs a process of receivingthe transmission data.

It is an object of the present invention to provide a communicationsystem, a communication device, and a communication method wherein thetransmission efficiency can be easily improved even when an accesssystem that does not detect a collision in a bus-type network isadopted.

DISCLOSURE OF THE INVENTION

In the communication system according to one aspect of the presentinvention, a plurality of communication devices connected to atransmission line adjust transmission timing of data based on adetection result of a carrier signal of another communication device toprevent a collision between signals, there by performingtransmission/reception of the data. Each respective communication devicecomprise a transmission control unit which, when newly transmitting thedata, transmits the data to the transmission line at a random timerandomly representing a time existing after a first time elapses until asecond time elapses from a time when a carrier signal on thetransmission line is gone and, when transmitting a data whose priorityis high, transmits the data to the transmission line before the firsttime.

According to the above-mentioned aspect of this invention, thetransmission control unit, when newly transmitting the data, transmitsthe data to the transmission line at a random time randomly representinga time existing after a first time elapses until a second time elapsesfrom a time when a carrier signal on the transmission line is gone and,when transmitting a data whose priority is high, transmits the data tothe transmission line before the first time so as to avoid a collisionof the data whose priority is high.

In the communication system according to the above-mentioned aspect, thedata whose priority is high is ACK data representing a receptionconfirmation.

Thus, by setting the data whose priority is high as ACK datarepresenting a reception confirmation, a collision of the ACK data maybe avoided.

In the communication system according to the above-mentioned aspect, thedata whose priority is high is NACK data representing a non-receptionconfirmation with respect to reception of a series of data groups towhich sequence numbers are assigned.

Thus, by setting the data whose priority is high is NACK datarepresenting a non-reception confirmation with respect to reception of aseries of data groups to which sequence numbers are assigned, acollision of the NACK data may be avoided.

In the communication system according to another aspect of the presentinvention, a plurality of communication devices connected to atransmission line are divided into one master communication device andother slave communication devices to logically form a star-typeconnection and adjust transmission timing of data based on a detectionresult of a carrier signal of another communication device to prevent acollision between signals, thereby performing transmission/reception ofthe data via the master communication device. The master communicationdevice comprises a transmission control unit which, when newlytransmitting the data, transmits the data to the transmission line at arandom time randomly representing a time existing after a first timeelapses until a second time elapses from a time when a carrier signal onthe transmission line is gone and, when transmitting a data that hasbeen relayed, transmits the data to the transmission line before thefirst time.

According to the above-mentioned aspect of this invention, thetransmission control unit of the master communication device, when newlytransmitting the data, transmits the data to the transmission line at arandom time randomly representing a time existing after a first timeelapses until a second time elapses from a time when a carrier signal onthe transmission line is gone and, when transmitting a data that hasbeen relayed, transmits the data to the transmission line before thefirst time so as to avoid a collision of the data relayed.

In the communication system according to still another aspect of thepresent invention, a plurality of communication devices connected to atransmission line are divided into one master communication device andother slave communication devices to logically form a star-typeconnection and adjust transmission timing of data based on a detectionresult of a carrier signal of another communication device to prevent acollision between signals, thereby performing transmission/reception ofthe data via the master communication device. The master communicationdevice comprises a transmission control unit which, when newlytransmitting the data, transmits the data to the transmission line at arandom time randomly representing a time existing after a first timeelapses until a second time elapses from a time when a carrier signal onthe transmission line is gone and, when receiving a data that has beenrelayed, transmits ACK data representing a reception confirmation of thedata after the reception of the data is confirmed before the first timeand transmits the data relayed to the transmission line before the firsttime from a time when a carrier signal of the ACK data is gone.

According to the above-mentioned aspect of this invention, thetransmission control unit of the master communication device, when newlytransmitting the data, transmits the data to the transmission line at arandom time randomly representing a time existing after a first timeelapses until a second time elapses from a time when a carrier signal onthe transmission line is gone and, when receiving a data that has beenrelayed, transmits ACK data representing a reception confirmation of thedata after the reception of the data is confirmed before the first timeand transmits the data relayed to the transmission line before the firsttime from a time when a carrier signal of the ACK data is gone so as todecrease processes of ACK data in a series of transmission processes.

In the communication system according to still another aspect of thepresent invention, a plurality of communication devices connected to atransmission line are divided into one master communication device andother slave communication devices to logically form a star-typeconnection and adjust transmission timing of data based on a detectionresult of a carrier signal of another communication device to prevent acollision between signals, thereby performing transmission/reception ofthe data via the master communication device. The master communicationdevice comprises a transmission control unit which transmits the data tothe transmission line at a random time randomly representing a timeexisting after a first time elapses until a second time elapses from atime when a carrier signal on the transmission line is gone when newlytransmitting the data and, repeating processing in which the mastercommunication device transmits ACK data representing a receptionconfirmation of the data after the reception of the data is confirmedbefore the first time, transmits the multi-address data relayed to thetransmission line before the first time from a time when a carriersignal of the ACK data is gone, and transmits the multi-address databefore the first time from a time when a carrier signal of themulti-address data is gone in a case where multi-address data relayed isreceived.

According to the above-mentioned aspect of this invention, thetransmission control unit of the master communication device, when newlytransmitting the data, transmits the data to the transmission line at arandom time randomly representing a time existing after a first timeelapses until a second time elapses from a time when a carrier signal onthe transmission line is gone and, in a case where multi-address datarelayed is received, repeats processing in which the mastercommunication device transmits ACK data representing a receptionconfirmation of the data after the reception of the data is confirmedbefore the first time, transmits the multi-address data relayed to thetransmission line before the first time from a time when a carriersignal of the ACK data is gone, and transmits the multi-address databefore the first time from a time when a carrier signal of themulti-address data is gone so as to avoid a collision of themulti-address data.

In the communication system according to still another aspect of thepresent invention, a plurality of communication devices connected to atransmission line are divided into one master communication device andother slave communication devices to logically form a star-typeconnection and adjust transmission timing of data based on a detectionresult of a carrier signal of another communication device to prevent acollision between signals, thereby performing transmission/reception ofthe data via the master communication device. The communication devicecomprises a transmission control unit which transmits the data to thetransmission line at a random time randomly representing a time existingafter a first time elapses until a second time elapses from a time whena carrier signal on the transmission line is gone in a case where thecommunication device newly transmits data and, transmits collisionavoidance data that is arbitrary data generating a carrier signal on thetransmission line at a random time randomly representing a time existingafter a first time elapses until a second time elapses from a time whena carrier signal on the transmission line is gone in a case wheremulti-address data is transmitted and transmits the multi-address databefore the first time from a time when a carrier signal of the collisionavoidance data is gone, and the transmission control unit of the mastercommunication device, when receiving the multi-address data, repeatsprocessing in which the multi-address data is transmitted to thetransmission line before the first time from a time when the carriersignal of the multi-address data is gone.

According to the above-mentioned aspect of this invention, thetransmission control unit of the communication device, in a case wherethe communication device newly transmits data, transmits the data to thetransmission line at a random time randomly representing a time existingafter a first time elapses until a second time elapses from a time whena carrier signal on the transmission line is gone and, in a case wheremulti-address data is transmitted, transmits collision avoidance datathat is arbitrary data generating a carrier signal on the transmissionline at a random time randomly representing a time existing after afirst time elapses until a second time elapses from a time when acarrier signal on the transmission line is gone and transmits themulti-address data before the first time from a time when a carriersignal of the collision avoidance data is gone, and the transmissioncontrol unit of the master communication device, when receiving themulti-address data, repeats processing in which the multi-address datais transmitted to the transmission line before the first time from atime when the carrier signal of the multi-address data is gone so as toavoid even a collision of the data transmitted from the communicationdevice of the transmission source.

In the communication system according to still another aspect of thepresent invention, a plurality of communication devices connected to atransmission line are divided into one master communication device andother slave communication devices to logically form a star-typeconnection and adjust transmission timing of data based on a detectionresult of a carrier signal of another communication device to prevent acollision between signals, thereby performing transmission/reception ofthe data via the master communication device, the communication devicecomprises a transmission control unit which transmits the data to thetransmission line at a random time randomly representing a time existingafter a first time elapses until a second time elapses from a time whena carrier signal on the transmission line is gone in a case where thecommunication device newly transmits data and, transmits collisionavoidance data that is arbitrary data generating a carrier signal on thetransmission line at a random time randomly representing a time existingafter a first time elapses until a second time elapses from a time whena carrier signal on the transmission line is gone and transmits the datawhose priority is high before the first time from a time when a carriersignal of the collision avoidance data is gone when transmitting a datawhose priority is high, and the transmission control unit of the mastercommunication device, when the data whose priority is high is received,transmits the data whose priority is high to the transmission linebefore the first time from a time when the carrier signal of the datawhose priority is high is gone.

According to the above-mentioned aspect of this invention, thetransmission control unit of the communication device, in a case wherethe communication device newly transmits data, transmits the data to thetransmission line at a random time randomly representing a time existingafter a first time elapses until a second time elapses from a time whena carrier signal on the transmission line is gone and, when transmittinga data whose priority is high, transmits collision avoidance data thatis arbitrary data generating a carrier signal on the transmission lineat a random time randomly representing a time existing after a firsttime elapses until a second time elapses from a time when a carriersignal on the transmission line is gone and transmits the data whosepriority is high before the first time from a time when a carrier signalof the collision avoidance data is gone, and the transmission controlunit of the master communication device, when the data whose priority ishigh is received, transmits the data whose priority is high to thetransmission line before the first time from a time when the carriersignal of the data whose priority is high is gone so as to avoid acollision of the data whose priority is high.

The communication device according to still another aspect of thepresent invention is employed in a communication system in which aplurality of communication devices connected to a transmission lineadjust transmission timing of data based on a detection result of acarrier signal of another communication device to prevent a collisionbetween signals, there by performing transmission/reception of the data.The communication device comprises a transmission control unit whichtransmits the data to the transmission line at a random time randomlyrepresenting a time existing after a first time elapses until a secondtime elapses from a time when a carrier signal on the transmission lineis gone when newly transmitting the data and, transmits the data to thetransmission line before the first time when transmitting a data whosepriority is high.

According to the above-mentioned aspect of this invention, thetransmission control unit, when newly transmitting the data, transmitsthe data to the transmission line at a random time randomly representinga time existing after a first time elapses until a second time elapsesfrom a time when a carrier signal on the transmission line is gone and,when transmitting a data whose priority is high, transmits the data tothe transmission line before the first time.

The communication device according to still another aspect of thepresent invention is employed in a communication system in which aplurality of communication devices connected to a transmission lineadjust transmission timing of data based on a detection result of acarrier signal of another communication device to prevent a collisionbetween signals, there by performing transmission/reception of the data.The communication device comprises a transmission control unit whichtransmits the data to the transmission line at a random time randomlyrepresenting a time existing after a first time elapses until a secondtime elapses from a time when a carrier signal on the transmission lineis gone when newly transmitting the data and, transmits collisionavoidance data that is arbitrary data generating a carrier signal on thetransmission line at a random time randomly representing a time existingafter a first time elapses until a second time elapses from a time whena carrier signal on the transmission line is gone and transmits the datawhose priority is high to the transmission line before the first timefrom a time when a carrier signal of the collision avoidance data isgone when transmitting a data whose priority is high.

According to the above-mentioned aspect of this invention, thetransmission control unit, when newly transmitting the data, transmitsthe data to the transmission line at a random time randomly representinga time existing after a first time elapses until a second time elapsesfrom a time when a carrier signal on the transmission line is gone and,when transmitting a data whose priority is high, transmits collisionavoidance data that is arbitrary data generating a carrier signal on thetransmission line at a random time randomly representing a time existingafter a first time elapses until a second time elapses from a time whena carrier signal on the transmission line is gone and transmits the datawhose priority is high to the transmission line before the first timefrom a time when a carrier signal of the collision avoidance data isgone.

The communication method according to still another aspect of thisinvention is a method of performing transmission/reception of the dataamong a plurality of communication devices connected to a transmissionline adjust transmission timing of data based on a detection result of acarrier signal of another communication device to prevent a collisionbetween signals. The communication method comprises a data transmissionstep of, when newly transmitting the data, transmits the data to thetransmission line at a random time randomly representing a time existingafter a first time elapses until a second time elapses from a time whena carrier signal on the transmission line is gone and a priority datatransmission step of, in a case where a transmission request of datawhose priority is high is generated, transmits the data whose priorityis high to the transmission line before the first time.

According to the above-mentioned aspect of this invention, in the datatransmission step, when newly transmitting the data, the respectivecommunication devices transmit the data to the transmission line at arandom time randomly representing a time existing after a first timeelapses until a second time elapses from a time when a carrier signal onthe transmission line is gone, and in the priority data transmissionstep, in a case where a transmission request of data whose priority ishigh is generated, the data whose priority is high is transmitted to thetransmission line before the first time.

In the communication method according to the above-mentioned aspect, thedata whose priority is high is ACK data representing a receptionconfirmation.

Thus, by setting the data whose priority is high as ACK datarepresenting a reception confirmation, a collision of the ACK data maybe avoided.

In the communication method according to the above-mentioned aspect, thedata whose priority is high is NACK data representing a non-receptionconfirmation with respect to reception of a series of data groups towhich sequence numbers are assigned.

Thus, by setting the data whose priority is high is NACK datarepresenting a non-reception confirmation with respect to reception of aseries of data groups to which sequence numbers are assigned, acollision of the NACK data may be avoided.

The communication method according to still another aspect of thisinvention is a method of performing transmission/reception of the dataamong a plurality of communication devices connected to a transmissionline are divided into one master communication device and other slavecommunication devices to logically form a star-type connection andadjust transmission timing of data based on a detection result of acarrier signal of another communication device to prevent a collisionbetween signals via the master communication device. The communicationmethod comprises a data transmission step of, transmitting the data tothe master communication device at a random time randomly representing atime existing after a first time elapses until a second time elapsesfrom a time when a carrier signal on the transmission line is gone in acase where a slave communication device of a transmission sourcetransmits data whose transmission is requested; a data relay step inwhich the master communication device that has received the datareceives the data and transmits the data to a slave communication deviceof a transmission destination before the first time elapses from a timewhen a carrier signal of the data on the transmission line is gone; anACK transmission step in which the slave communication device of thetransmission destination transmits ACK data representing a receptionconfirmation to the master communication device after the reception ofthe data is confirmed before the first time; and an ACK relaytransmission step in which the master communication device that hasreceived the ACK data receives the ACK data and transmits the ACK datato the slave communication device of the transmission source before thefirst time elapses from a time when a carrier signal of the ACK data onthe transmission line is gone.

According to the above-mentioned aspect of this invention, in the datatransmission step, in a case where a slave communication device of atransmission source transmits data whose transmission is requested, thedata is transmitted to the master communication device at a random timerandomly representing a time existing after a first time elapses until asecond time elapses from a time when a carrier signal on thetransmission line is gone, in the data relay step, the mastercommunication device that has received the data receives the data andtransmits the data to a slave communication device of a transmissiondestination before the first time elapses from a time when a carriersignal of the data on the transmission line is gone, in the ACKtransmission step, the slave communication device of the transmissiondestination transmits ACK data representing a reception confirmation tothe master communication device after the reception of the data isconfirmed before the first time, and in the ACK relay transmission step,the master communication device that has received the ACK data receivesthe ACK data and transmits the ACK data to the slave communicationdevice of the transmission source before the first time elapses from atime when a carrier signal of the ACK data on the transmission line isgone.

The communication method according to still another aspect of thisinvention is a method of performing transmission/reception of the dataamong a plurality of communication devices connected to a transmissionline are divided into one master communication device and other slavecommunication devices to logically form a star-type connection andadjust transmission timing of data based on a detection result of acarrier signal of another communication device to prevent a collisionbetween signals via the master communication device. The communicationmethod comprises a data transmission step of transmitting the data tothe master communication device at a random time randomly representing atime existing after a first time elapses until a second time elapsesfrom a time when a carrier signal on the transmission line is gone in acase where a slave communication device of a transmission sourcetransmits data whose transmission is requested, an ACK transmission stepin which the master communication device that has received the datatransmits ACK data representing a reception confirmation to the slavecommunication device of the transmission source after the reception ofthe data is confirmed before the first time, and a data relaytransmission step in which the master communication device transmits thedata to a slave communication device of a transmission destination afterthe transmission of the ACK data before the first time from a time whena carrier signal of the ACK data is gone.

According to the above-mentioned aspect of this invention, in the datatransmission step, in a case where a slave communication device of atransmission source transmits data whose transmission is requested, thedata is transmitted to the master communication device at a random timerandomly representing a time existing after a first time elapses until asecond time elapses from a time when a carrier signal on thetransmission line is gone, in the ACK transmission step, the mastercommunication device that has received the data transmits ACK datarepresenting a reception confirmation to the slave communication deviceof the transmission source after the reception of the data is confirmedbefore the first time, and in the data relay transmission step, themaster communication device transmits the data to a slave communicationdevice of a transmission destination after the transmission of the ACKdata before the first time from a time when a carrier signal of the ACKdata is gone.

The communication method according to still another aspect of thisinvention is a method of performing transmission/reception of the dataamong a plurality of communication devices connected to a transmissionline are divided into one master communication device and other slavecommunication devices to logically form a star-type connection andadjust transmission timing of data based on a detection result of acarrier signal of another communication device to prevent a collisionbetween signals via the master communication device. The communicationmethod comprises a multi-address data transmission step of transmittingthe multi-address data to the master communication device at a randomtime randomly representing a time existing after a first time elapsesuntil a second time elapses from a time when a carrier signal on thetransmission line is gone in a case where a slave communication deviceof a transmission source transmits multi-address data whose transmissionis requested, an ACK transmission step in which the master communicationdevice that has received the multi-address data transmits ACK datarepresenting a reception confirmation to the slave communication deviceof the transmission source after the reception of the multi-address datais confirmed before the first time, and a multi-address data relaytransmission step of repeating processing in which the mastercommunication device transmits the multi-address data to a slavecommunication device of a transmission destination after thetransmission of the ACK data before the first time from a time when acarrier signal of the ACK data is gone and transmits the multi-addressdata to a slave communication device of a transmission destinationbefore the first time from a time when a carrier signal of themulti-address data is gone.

According to the above-mentioned aspect of this invention, in themulti-address data transmission step, in a case where a slavecommunication device of a transmission source transmits multi-addressdata whose transmission is requested, the multi-address data istransmitted to the master communication device at a random time randomlyrepresenting a time existing after a first time elapses until a secondtime elapses from a time when a carrier signal on the transmission lineis gone, in the ACK transmission step, the master communication devicethat has received the multi-address data transmits ACK data representinga reception confirmation to the slave communication device of thetransmission source after the reception of the multi-address data isconfirmed before the first time, and in the multi-address data relaytransmission step, the master communication device repeats processing inwhich the master communication device transmits the multi-address datato a slave communication device of a transmission destination after thetransmission of the ACK data before the first time from a time when acarrier signal of the ACK data is gone and transmits the multi-addressdata to a slave communication device of a transmission destinationbefore the first time from a time when a carrier signal of themulti-address data is gone.

The communication method according to still another aspect of thisinvention is a method of performing transmission/reception of the dataamong a plurality of communication devices connected to a transmissionline are divided into one master communication device and other slavecommunication devices to logically form a star-type connection andadjust transmission timing of data based on a detection result of acarrier signal of another communication device to prevent a collisionbetween signals, thereby performing transmission/reception of the datavia the master communication device, the communication method comprisesa collision avoidance data transmission step of transmitting collisionavoidance data that is arbitrary data generating a carrier signal on thetransmission line at a random time randomly representing a time existingafter a first time elapses until a second time elapses from a time whena carrier signal on the transmission line is gone in a case where aslave communication device of a transmission source transmitsmulti-address data whose transmission is requested, a multi-address datarelay transmission step in which the slave communication device of thetransmission source transmits the multi-address data to the mastercommunication device before the first time from a time when a carriersignal of the collision avoidance data is gone, and an multi-addressdata relay transmission step of repeating processing in which the mastercommunication device that has received the multi-address data transmitsthe multi-address data to a slave communication device of a transmissiondestination before the first time from a time when a carrier signal ofthe multi-address data is gone and transmits the multi-address data to aslave communication device of a transmission destination before thefirst time from a time when a carrier signal of the multi-address datais gone.

According to the above-mentioned aspect of this invention, in thecollision avoidance data transmission step, in a case where a slavecommunication device of a transmission source transmits multi-addressdata whose transmission is requested, collision avoidance data that isarbitrary data generating a carrier signal on the transmission line istransmitted at a random time randomly representing a time existing aftera first time elapses until a second time elapses from a time when acarrier signal on the transmission line is gone, in the multi-addressdata relay transmission step, the slave communication device of thetransmission source transmits the multi-address data to the mastercommunication device before the first time from a time when a carriersignal of the collision avoidance data is gone, and in the multi-addressdata relay transmission step, the master communication device repeatsprocessing in which the master communication device that has receivedthe multi-address data transmits the multi-address data to a slavecommunication device of a transmission destination before the first timefrom a time when a carrier signal of the multi-address data is gone andtransmits the multi-address data to a slave communication device of atransmission destination before the first time from a time when acarrier signal of the multi-address data is gone so as to avoid even acollision of the data transmitted from the communication device of thetransmission source.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is views illustrating the structure of a communication system andaccess control processing according to a first embodiment of the presentinvention;

FIG. 2 is a sequence chart illustrating access control processing of acommunication system according to a second embodiment of the presentinvention;

FIG. 3 is block diagrams illustrating the structure of a communicationsystem according to a third embodiment of the present invention;

FIG. 4 is a sequence chart illustrating access control processing of acommunication system according to the third embodiment of the presentinvention;

FIG. 5 is a sequence chart illustrating access control processing of acommunication system according to a fourth embodiment of the presentinvention;

FIG. 6 is a sequence chart illustrating access control processing of acommunication system according to a fifth embodiment of the presentinvention;

FIG. 7 is a sequence chart illustrating access control processing of acommunication system according to a sixth embodiment of the presentinvention; and

FIG. 8 is views illustrating the structure of a conventionalcommunication system and access control processing in which the CSMA/CDsystem is employed.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the communication system, the communication device, andthe communication method in accordance with the present invention willbe explained in detail below while referring to the accompanyingdrawings.

First Embodiment:

FIG. 1 is a block diagram illustrating the structure of a communicationsystem and the access control thereof according to a first embodiment ofthe present invention. FIG. 1( a) shows the structure of thecommunication system, FIG. 1( b) shows one example of datatransmission/reception between a node N1 and a node N2, and FIG. 1( c)shows a timing chart explaining the access control by nodes N1 to N3. InFIG. 1, in this communication system, the plural nodes N1 to N3 areconnected to a transmission line N, such as a power line, in a bus-typemanner. The respective nodes N1 to N3 can detect a carrier signal on thetransmission line N but cannot detect a collision.

In general, in a transmission/reception process of data, a node of areception side which has received transmission data sends back ACK datashowing whether or not the data is normally received to the node of atransmission source. For example, as shown in FIG. 1( b), when the nodeN1 transmits data D11 to the node N2, the node N2 sends back ACK dataD12 of reception confirmation showing that the data is normally receivedto the node N1.

In the present communication system, since the respective nodes N1 to N3cannot detect a collision, the respective nodes N1 to N3 perform accesscontrol shown in FIG. 1( c). In FIG. 1( c), a case is considered where atransmission request of data is generated at the node N3 at a time pointT0 while the node N1 transmits data D11 to the transmission line N. Thenode N3 detects the carrier of the data D11 and sets a time point T3present between the time after a time t1 taking a time point T1 as anorigin point elapses and a time t2, that is after the time point T1where the carrier of the data D11 is gone, as a waiting time generatedby random number generation.

The node N2 which has received the data D11 detects “EOF” or the likerepresenting the end of real data in the data D11 to confirm receptionand sends out the ACK data D12 for the data D11 to the transmission lineN at a time point T2 before a time t1 after the time T1 to send it tothe node N1. Therefore, the ACK data D12 can be transmitted havingpriority over general data D13, and through the transmission of the ACKdata D12, the node N3 tries to transmit the data D13 at a time point T5set within a certain period of time before a time t2 after a time t1elapses from a time point T4 at which the carrier of the ACK data D12 isgone again.

That is, the general data, after detecting that the carrier is gone,cannot be transmitted for a certain period of time of t1, and only theACK data D12 is sent during the certain period of time t1. Thus, acollision of the ACK data can be reliably avoided, and sinceretransmission of transmission data due to the collision of the ACK datais not needed, the transmission efficiency is improved remarkably.Specifically, in a case where a transmission of data whose data lengthis long succeeds, when ACK data whose length is short collides, atransmission line N is occupied in a time span in the retransmission ofthe data whose data length is long. However, in the first embodiment,since the ACK data does not collide, the transmission efficiency isimproved remarkably. Since the waiting time of general data is generatedby random numbers, a collision hardly occurs. However, when waitingtimes are nearly the same time, a collision occurs.

Besides ACK data, when transmitting a data whose priority is high, bytransmitting the data whose priority is high during the certain periodof time t1 from the time when the carrier on the transmission line N isgone similarly to the case of ACK data, a collision of the data whosepriority is high can be reliably avoided. When both of a collision ofACK data and a collision of data whose priority is high should beavoided, the certain period of time t1 may further be divided, and therespective divided times may be allocated to the each data.

In the first embodiment, waiting time decided by random numbers is notset during a certain period of time starting from the time when acarrier on the transmission line N is gone, but waiting time decided byrandom numbers is set from a point in time when the certain period oftime t1 elapses from the time when a carrier on the transmission line Nis gone. In this waiting time, transmission permission for general datais performed, and transmission of ACK data is permitted in the certainperiod of time t1 from the time when a carrier on the transmission lineN is gone. Thus, a collision of ACK data can be reliably avoided, andtherefore the transmission efficiency can be improved remarkably.

Second Embodiment:

Next, a second embodiment of the present invention is explained.Although the first embodiment described above is to reliably avoid acollision of ACK data, the second embodiment is to reliably avoid acollision of NACK data that is for retransmitting part of data in a casewhere a series of data is transmitted and when the part of data in theseries of data cannot be received normally.

FIG. 2 is a sequence chart explaining access control by a communicationsystem according to the second embodiment of the present invention. Thestructure of the communication system is the same as that of the firstembodiment. Here, a case is considered where the node N1 divides datawhose data length is long into four data (1) to data (4) to transmitthem as a series of data. A series of sequence numbers is assigned tothe respective data (1) to data (4). In FIG. 2, the node N1 firsttransmits data D21 of the data (1) to the node N2 at a time point aftera certain period of time t1 elapses from a time point when a carrier onthe transmission line N is gone. A similar waiting time is set so thatthe data (2) to the data (4) are transmitted to the node N2 as data D22to D24 one after another.

Here, in a case where data D23 of the data (3) collides, when the nodeN2 detects that the node N2 could not normally received the data (3) ofsequence number “3,” the node N2 sends back NACK data D25, representingthat the data (3) could not be received, to the node N1 after receivingdata D24 that is final series data (4) before the certain period of timet1 from a time point when the carrier of the data D24 is gone. Since theNACK data D25 is transmitted as the only data within the certain periodof time t1 that is shorter than a general waiting time period, a collidecan be reliably avoided similarly to the case of ACK data in the firstembodiment.

The node N1 that has received the NACK data D25 transmits data (3) thatcorresponds to the sequence number “3” shown in the NACK data D25 to thenode N2 as data D26. Thereafter, when the node N2 receives all of theseries of data in the end, the node N2 transmits ACK data D27 to thenode N1 side before the certain period of time t1 similarly to the firstembodiment.

In the second embodiment, in a case where a series of data istransmitted sequentially, when part of data of the series of data couldnot be received normally, since NACK data is sent back after the finalseries of data is received before the certain period of time t1, acollision of NACK data can be reliably avoided, and retransmission of aseries of data is not needed, whereby the transmission efficiency can beremarkably improved.

Third Embodiment:

Next, a third embodiment of the present invention is explained. In thethird embodiment, one node among nodes constituting a bus-type networkis set as a master node, other nodes are set as slave nodes to form alogical star network, each of the master node and the respective slavenodes transmit/receive data, and the access control shown in the firstembodiment described above is applied to the communication system inwhich data transmission/reception is performed among the respectiveslave nodes via the master node so as to improve the transmissionefficiency.

FIG. 3 is diagrams illustrating the structure of a communication systemaccording to the third embodiment of the present invention. FIG. 3( a)is a diagram illustrating the physical structure of the communicationsystem, and FIG. 3( b) is a diagram illustrating the logical structureof the communication system shown in FIG. 3( a). In FIG. 3, in thecommunication system, a plurality of nodes N10 to N13 are connected tothe transmission line N in a bus-type connection, the node N10 in thenodes N10 to N13 is set as a master node, and the nodes N11 to N13 areset as slave nodes connected to the master node N10 in a star-typeconnection. The respective slave nodes N11 to N13 transmit/receive datato/from the master node N10, and the transmission/reception of dataamong the respective slave nodes N11 to N13 is performed via the masternode N10.

Here, a process in which the slave node N11 transmits data to the slavenode N12 is explained referring to a sequence chart shown in FIG. 4. Thetransmission/reception of data between the master node N10 and therespective slave nodes N11 to N13 is performed similarly to that of thefirst embodiment. In FIG. 4, when a transmission request of data isgenerated, the slave node N11 that is a transmission source of datatransmits data D31 to the master node N10 after the waiting time afterthe certain period of time t1 similarly to the case of the general datashown in the first embodiment.

The master node N10 that has received the data D31 transmits data D32relaying the data D31 to the slave node N12 before the certain period oftime t1. Further, the slave node N12 that has received data D32transmits ACK data D33 with respect to data D32 to the master node N10before the certain period of time t1. Thereafter, the master node N10that has received the ACK data D33 transmits ACK data D34 relaying theACK data D33 to the slave node N11 before the certain period of time t1.

In this case, since all data D32 to D34 are transmitted before thecertain period of time t1, a collision between the all data and generaldata can be reliably avoided, and a collision is not generated in aseries of data transmission/reception sequences.

When receiving the data D31 and the ACK data D33, the master node N10only relays the received data, transmits simply as data D32 and ACK dataD34, and does not confirm the content received. Therefore, in the masternode N10 a buffer for data relaying is not needed.

In the third embodiment, when transmission/reception of a series of datais performed among the slave node N11 to N13 via the master node N10,since data is transmitted after all carriers are gone before the certainperiod of time t1 during the transmission/reception of the series ofdata, a collision of the series of data can be reliably avoided.

Fourth Embodiment:

Next, a fourth embodiment of the present invention is explained.Although as many as four steps of transmission processes are performedin the case where transmission/reception of a series of data isperformed among the slave nodes N11 to N13 in the third embodimentdescribed above, transmission processes are reduced to three steps inthe fourth embodiment to enhance the transmission efficiency.

The structure of the communication system of the fourth embodiment isthe same as that of the third embodiment. Here, a process in which theslave node N11 transmits data to the slave node N12 is explainedreferring to a sequence chart shown in FIG. 5. When a transmissionrequest of data is generated, the slave node N11 that is a transmissionsource of data transmits data D41 to the master node N10 after thewaiting time after the certain period of time t1 similarly to the caseof the general data shown in the first embodiment.

The master node N10 that has received the data D41 confirms thereception of the data D41 and sends back ACK data D42 to the slave nodeN11 before the certain period of time t1. Thereafter, the master nodeN10 transmits data D43 relaying the data D41 to the slave node N12. Thedata D43 is transmitted after the transmission of the ACK data D42before the certain period of time t1.

In this case, although the master node N10 confirms the reception of thedata D41 which is relayed and received, one step of transmissionprocesses of ACK data is eliminated in a series of data sequencescompared to the third embodiment.

In the fourth embodiment, when a series of data transmissions/receptionsis performed among the slave nodes N11 to N13 via the master node N10,since data is transmitted after all carriers are gone before the certainperiod of time t1 during the transmission/reception of the series ofdata, a collision of the series of data can be reliably avoided, andtransmission processes for the transmission of the series of data can bedecreased.

Fifth Embodiment:

Next, a fifth embodiment of the present invention is explained. Fifthembodiment is to improve the transmission efficiency in a case wheremulti-address data is transmitted in the fourth embodiment.

The structure of the communication system of the fifth embodiment is thesame as that of the third embodiment. Here, a process in which the slavenode N11 transmits multi-address data to the slave nodes N12, N13 isexplained referring to a sequence chart shown in FIG. 6. When atransmission request of multi-address data is generated, the slave nodeN11 that is a transmission source of data transmits multi-address dataD51 to the master node N10 after the waiting time after the certainperiod of time t1 similarly to the case of the general data shown in thefirst embodiment.

The master node N10 that has received the multi-address data D51confirms the reception of the data D51 and sends back ACK data D52 tothe slave node N11 before the certain period of time t1. Thereafter, themaster node N10 transmits multi-address data D53, D54 that relay thedata D51 in a multiple address form to the slave nodes N12, N13. Thedata D53 is transmitted after the transmission of the ACK data D52before the certain period of time t1. The data D54 is transmitted afterthe transmission of the data D53 before the certain period of time t1.

In the fifth embodiment, corresponding to the fourth embodiment,although only the master node N10 transmits the ACK data D52 to theslave node N11, the invention is not limited to this, and correspondingto the third embodiment, the respective slave nodes that have receivedthe multi-address data may transmit ACK data to the master node N10before the certain period of time t1 so that the master node N10 cantransmit the respective ACK data to the slave node of the transmissionsource, or ACK data is transmitted to the slave node of the transmissionsource when the master node N10 receives ACK data from all slave nodesof the transmission sources. In this case, all data is transmittedbefore the certain period of time t1.

In the fifth embodiment, since data is transmitted after all carriersare gone before the certain period of time t1 during thetransmission/reception of a series of data even when thetransmission/reception of multi-address data is performed among theslave nodes N11 to N13 via the master node N10, a collision of theseries of data can be reliably avoided.

Sixth Embodiment:

Next, a sixth embodiment of the present invention is explained. Althoughdata is transmitted after the waiting time after the certain period oftime t1 when a slave node of a transmission source transmits data in anyof the third embodiment to the fifth embodiment described above, eventhe first data collision can be reliably avoided in the sixthembodiment.

The structure of the communication system of the sixth embodiment is thesame as that of the third embodiment. Here, a process in which the slavenode N11 transmits multi-address data to the slave nodes N12, N13 isexplained referring to a sequence chart shown in FIG. 7. When atransmission request of multi-address data is generated, the slave nodeN11 that is a transmission source of data transmits collision avoidancedata D61 to the master node N10 after the waiting time after the certainperiod of time t1 similarly to the case of the general data shown in thefirst embodiment. The content of the collision avoidance data D61 isarbitrary and may be one by which a carrier can be generated on thetransmission line N.

By the transmission of the collision avoidance data D61 to thetransmission line N, other nodes detect a carrier, and when data istransmitted, the waiting time after the certain period of time t1 is setsimilarly to the case of the general data. The slave node N11 transmitsmulti-address data D62 to the master node N10 after the carrier of thecollision avoidance data D61 is gone before the certain period of timet1. Accordingly, the multi-address data D62 avoids a collision and isreliably transmitted to the master node N10.

The master node N10 that has received the multi-address data D62transmits the multi-address data D63 that relays multi-address data 62in a multiple address form to the slave node N12 after the carrier ofthe multi-address data D62 is gone before the certain period of time t1.Further, the master node N10 transmits the multi-address data D64 to theslave node N13 after the transmission of the multi-address data D63before the certain period of time t1.

In this case, ACK data is not needed, and the master node N10 or theslave nodes N12, N13 do not need to confirm reception. Since a collisionof the multi-address data 62 is also avoided reliably by the collisionavoidance data D61, a series of transmission processes can be performedreliably without any collision.

Although a case of the transmission of multi-address data is explainedin the sixth embodiment described above, the present invention is notlimited to this case, and even in a case of one-to-onetransmission/reception, by transmitting the collision avoidance data D61before data transmission and by transmitting data after the transmissionof the collision avoidance data D61 before the certain period of timet1, a collision of all data in the transmission processes of the datacan be avoided.

Even in a case where the master node N10 independently transmits data toanother slave node, by transmitting the collision avoidance data D61, acollision of data can be reliably avoided. In this case, the master nodeN10 and the slave nodes N11 to N13 may hold the same transmissionprotocol.

In the sixth embodiment, since the collision avoidance data D61 istransmitted before a series of multi-address data transmission processesto perform transmission while forcibly avoiding a collision of themulti-address data D62, a collision of all data in a series ofmulti-address data transmission processes can be reliably avoided.

As described above, with the present invention, since the transmissioncontrol unit, in a case where new transmission of data, transmits thedata to the transmission line at a random time randomly representing atime existing after a first time elapses until a second time elapsesfrom a time when a carrier signal on the transmission line is gone and,when transmitting a data whose priority is high, transmits the data tothe transmission line before the first time so as to avoid a collisionof the data whose priority is high, produced is an effect that thetransmission efficiency can be improved by a simple structure in which acollision is not detected.

With the next invention, since the data whose priority is high is set asACK data representing a reception confirmation to avoid a collision ofthe ACK data, produced is an effect that reduction of the transmissionefficiency due to retransmission of transmission data can be prevented.

With the next invention, since the data whose priority is high is set asNACK data representing a non-reception confirmation with respect toreception of a series of data groups to which sequence numbers areassigned to avoid a collision of the NACK data, all of a series of datagroups does not have to be retransmitted, whereby produced is an effectthat the transmission efficiency is improved.

With the next invention, since the transmission control unit of thecommunication device, when newly transmitting the data, transmits thedata to the transmission line at a random time randomly representing atime existing after a first time elapses until a second time elapsesfrom a time when a carrier signal on the transmission line is gone and,when transmitting a data that has been relayed, transmits the data tothe transmission line before the first time so as to avoid a collisionof the data relayed, a collision of relay data can be reliably avoided,and reception confirmation of data is not performed, whereby produced isan effect that data buffer at a time of relaying is not needed so thatthe structure can be made simple.

With the next invention, since the transmission control unit of themaster communication device, when newly transmitting the data, transmitsthe data to the transmission line at a random time randomly representinga time existing after a first time elapses until a second time elapsesfrom a time when a carrier signal on the transmission line is gone and,when receiving a data that has been relayed, transmits ACK datarepresenting a reception confirmation of the data after the reception ofthe data is confirmed before the first time and transmits the datarelayed to the transmission line before the first time from a time whena carrier signal of the ACK data is gone so as to decrease processes ofACK data in a series of transmission processes, produced is an effectthat the data transmission processes become simple so that thetransmission efficiency can be improved.

With the next invention, since the transmission control unit of themaster communication device, when newly transmitting the data, transmitsthe data to the transmission line at a random time randomly representinga time existing after a first time elapses until a second time elapsesfrom a time when a carrier signal on the transmission line is gone and,in a case where multi-address data relayed is received, repeatsprocessing in which the master communication device transmits ACK datarepresenting a reception confirmation of the data after the reception ofthe data is confirmed before the first time, transmits the multi-addressdata relayed to the transmission line before the first time from a timewhen a carrier signal of the ACK data is gone, and transmits themulti-address data before the first time from a time when a carriersignal of the multi-address data is gone so as to avoid a collision ofthe multi-address data, a collision of the multi-address data can beavoided even in a case where multi-address data with a large number oftransmission processes is transmitted, whereby produced is an effectthat the transmission efficiency can be improved.

With the next invention, since the transmission control unit of themaster communication device, in a case where the communication devicenewly transmits data, transmits the data to the transmission line at arandom time randomly representing a time existing after a first timeelapses until a second time elapses from a time when a carrier signal onthe transmission line is gone and, in a case where multi-address data istransmitted, transmits collision avoidance data that is arbitrary datagenerating a carrier signal on the transmission line at a random timerandomly representing a time existing after a first time elapses until asecond time elapses from a time when a carrier signal on thetransmission line is gone and transmits the multi-address data beforethe first time from a time when a carrier signal of the collisionavoidance data is gone, and the transmission control unit of the mastercommunication device, when receiving the multi-address data, repeatsprocessing in which the multi-address data is transmitted to thetransmission line before the first time from a time when the carriersignal of the multi-address data is gone so as to avoid even a collisionof the data transmitted from the communication device of thetransmission source, produced are effects that reliable datatransmission can be performed and the transmission efficiency can befurther improved.

With the next invention, since the transmission control unit of themaster communication device, in a case where the communication devicenewly transmits data, transmits the data to the transmission line at arandom time randomly representing a time existing after a first timeelapses until a second time elapses from a time when a carrier signal onthe transmission line is gone and, when transmitting a data whosepriority is high, transmits collision avoidance data that is arbitrarydata generating a carrier signal on the transmission line at a randomtime randomly representing a time existing after a first time elapsesuntil a second time elapses from a time when a carrier signal on thetransmission line is gone and transmits the data whose priority is highbefore the first time from a time when a carrier signal of the collisionavoidance data is gone, and the transmission control unit of the mastercommunication device, when the data whose priority is high is received,transmits the data whose priority is high to the transmission linebefore the first time from a time when the carrier signal of the datawhose priority is high is gone so as to avoid a collision of the datawhose priority is high, produced is an effect that data whose priorityis high can be reliably transmitted.

With the next invention, since the transmission control unit, when newlytransmitting the data, transmits the data to the transmission line at arandom time randomly representing a time existing after a first timeelapses until a second time elapses from a time when a carrier signal onthe transmission line is gone and, when transmitting a data whosepriority is high, transmits the data to the transmission line before thefirst time, produced is an effect that even by a simple structure inwhich a collision is not detected, the transmission efficiency can beimproved.

With the next invention, since the transmission control unit, when newlytransmitting the data, transmits the data to the transmission line at arandom time randomly representing a time existing after a first timeelapses until a second time elapses from a time when a carrier signal onthe transmission line is gone and, when transmitting a data whosepriority is high, transmits collision avoidance data that is arbitrarydata generating a carrier signal on the transmission line at a randomtime randomly representing a time existing after a first time elapsesuntil a second time elapses from a time when a carrier signal on thetransmission line is gone and transmits the data whose priority is highto the transmission line before the first time from a time when acarrier signal of the collision avoidance data is gone, produced is aneffect that a collision of all data in the data transmission processescan be avoided.

With the next invention, in the data transmission step, when newlytransmitting the data, the respective communication devices transmit thedata to the transmission line at a random time randomly representing atime existing after a first time elapses until a second time elapsesfrom a time when a carrier signal on the transmission line is gone, andin the priority data transmission step, in a case where a transmissionrequest of data whose priority is high is generated, the data whosepriority is high is transmitted to the transmission line before thefirst time. Thus, produced is an effect that even not in a case where acarrier on the transmission line is detected to detect a collision, acollision of data whose priority is high can be reliably avoided so thatthe transmission efficiency can be improved.

With the next invention, since the data whose priority is high is set asACK data representing a reception confirmation to avoid a collision ofthe ACK data, produced is an effect that reduction of the transmissionefficiency due to retransmission of transmission data can be prevented.

With the next invention, since the data whose priority is high is set asNACK data representing a non-reception confirmation with respect toreception of a series of data groups to which sequence numbers areassigned to avoid a collision of the NACK data, all of a series of datagroups does not have to be retransmitted, whereby produced is an effectthat the transmission efficiency is improved.

With this invention, in the data transmission step, in a case where aslave communication device of a transmission source transmits data whosetransmission is requested, the data is transmitted to the mastercommunication device at a random time randomly representing a timeexisting after a first time elapses until a second time elapses from atime when a carrier signal on the transmission line is gone, in the datarelay step, the master communication device that has received the datareceives the data and transmits the data to a slave communication deviceof a transmission destination before the first time elapses from a timewhen a carrier signal of the data on the transmission line is gone, inthe ACK transmission step, the slave communication device of thetransmission destination transmits ACK data representing a receptionconfirmation to the master communication device after the reception ofthe data is confirmed before the first time, and in the ACK relaytransmission step, the master communication device that has received theACK data receives the ACK data and transmits the ACK data to the slavecommunication device of the transmission source before the first timeelapses from a time when a carrier signal of the ACK data on thetransmission line is gone. Thus, produced are effects that a collisionof relay data can be reliably avoided, and simple relay processing canbe performed since reception confirmation of data is not performed.

With the next invention, in the a data transmission step, in a casewhere a slave communication device of a transmission source transmitsdata whose transmission is requested, the data is transmitted to themaster communication device at a random time randomly representing atime existing after a first time elapses until a second time elapsesfrom a time when a carrier signal on the transmission line is gone, inthe ACK transmission step, the master communication device that hasreceived the data transmits ACK data representing a receptionconfirmation to the slave communication device of the transmissionsource after the reception of the data is confirmed before the firsttime, and in the data relay transmission step, the master communicationdevice transmits the data to a slave communication device of atransmission destination after the transmission of the ACK data beforethe first time from a time when a carrier signal of the ACK data isgone. Thus, produced is an effect that the data transmission processesbecomes simple so that the transmission efficiency can be improved.

With the next invention, in the multi-address data transmission step, ina case where a slave communication device of a transmission sourcetransmits multi-address data whose transmission is requested, themulti-address data is transmitted to the master communication device ata random time randomly representing a time existing after a first timeelapses until a second time elapses from a time when a carrier signal onthe transmission line is gone, in the ACK transmission step, the mastercommunication device that has received the multi-address data transmitsACK data representing a reception confirmation to the slavecommunication device of the transmission source after the reception ofthe multi-address data is confirmed before the first time, and in themulti-address data relay transmission step, the master communicationdevice repeats processing in which the master communication devicetransmits the multi-address data to a slave communication device of atransmission destination after the transmission of the ACK data beforethe first time from a time when a carrier signal of the ACK data is goneand transmits the multi-address data to a slave communication device ofa transmission destination before the first time from a time when acarrier signal of the multi-address data is gone. Thus, produced is aneffect that even in a case where multi-address data with a large numberof transmission processes is transmitted, a collision of themulti-address data can be avoided so that the transmission efficiencycan be improved.

With the next invention, in the collision avoidance data transmissionstep, in a case where a slave communication device of a transmissionsource transmits multi-address data whose transmission is requested,collision avoidance data that is arbitrary data generating a carriersignal on the transmission line is transmitted at a random time randomlyrepresenting a time existing after a first time elapses until a secondtime elapses from a time when a carrier signal on the transmission lineis gone, in the multi-address data relay transmission step, the slavecommunication device of the transmission source transmits themulti-address data to the master communication device before the firsttime from a time when a carrier signal of the collision avoidance datais gone, and in the multi-address data relay transmission step, themaster communication device repeats processing in which the mastercommunication device that has received the multi-address data transmitsthe multi-address data to a slave communication device of a transmissiondestination before the first time from a time when a carrier signal ofthe multi-address data is gone and transmits the multi-address data to aslave communication device of a transmission destination before thefirst time from a time when a carrier signal of the multi-address datais gone so as to avoid even a collision of the data transmitted from thecommunication device of the transmission source. Thus, produced areeffects that reliable data transmission can be performed and thetransmission efficiency can be further improved.

INDUSTRIAL APPLICABILITY

As described above, in the communication systems, the communicationdevices, and the communication methods according to the presentinvention, a plurality of communication devices connected to atransmission line adjust transmission timing of data based on adetection result of a carrier signal of another communication device,and thus the present invention is suitable for prevention of a collisionbetween signals.

1. A communication system comprising: a plurality of communicationdevices being connected to a transmission line and divided into onemaster communication device and other slave communication devices tologically form a star-type connection and adjusting transmission timingof data based on a detection result of a carrier signal of anothercommunication device to prevent a collision between signals, therebyperforming transmission or reception of the data via the mastercommunication device, wherein the data includes first multi-address datato be relayed, ACK data representing a reception confirmation of thefirst multi-address data, second multi-address data for relaying thefirst multi-address data, third multi-address data for relaying thefirst multi-address data, and general data, the master communicationdevice includes a transmission control unit configured to transmit thegeneral data at a random time determined by random numbers set afterelapse of a first time and before elapse of a second time from a timewhen the carrier signal on the transmission line is gone, when newlytransmitting the data, and to transmit the ACK data to the transmissionline before elapse of the first time from a time when the mastercommunication device confirms reception of the first multi-address dataand, when the first multi-address data is received, to transmit thesecond multi-address data to the transmission line before elapse of thefirst time from a time when a carrier signal of the ACK data is gone,and to subsequently transmit the third multi-address data before elapseof the first time from a time when a carrier signal of the secondmulti-address data is gone.
 2. A communication system comprising: aplurality of communication devices being connected to a transmissionline and divided into one master communication device and other slavecommunication devices to logically form a star-type connection andadjusting transmission timing of data based on a detection result of acarrier signal of another communication device to prevent a collisionbetween signals, thereby performing transmission or reception of thedata via the master communication device, wherein the data includesfirst multi-address data to be relayed, collision avoidance data that isarbitrary data for generating a carrier signal on the transmission line,second multi-address data for relaying the first multi-address data,third multi-address data for relaying the first multi-address data andgeneral data, each of the plurality of communication devices includes atransmission control unit configured to transmit the general data at arandom time determined by random numbers set after elapse of a firsttime and before elapse of a second time from a time when the carriersignal on the transmission line is gone, when newly transmitting thedata, to transmit the collision avoidance data at a random timedetermined by random numbers set after elapse of the first time andbefore elapse of the second time from a time when the carrier signal onthe transmission line is gone, when transmitting the multi-address data,and to transmit the multi-address data before elapse of the first timefrom a time when a carrier signal of the collision avoidance data isgone, when the multi-address data is transmitted, wherein a transmissioncontrol unit of the master communication device, when receiving thefirst multi-address data, transmits the second multi-address data to thetransmission line before elapse of the first time from a time when acarrier signal of the first multi-address data is gone, and subsequentlytransmit the third multi-address data before elapse of the first time.3. A communication method in which a plurality of communication devicesare connected to a transmission line and divided into one mastercommunication device and other slave communication devices to logicallyform a star-type connection and adjust transmission timing of data basedon a detection result of a carrier signal of another communicationdevice to prevent a collision between signals, thereby performingtransmission or reception of the data via the master communicationdevice, wherein the data includes first data whose transmission isrequested and ACK data representing a reception confirmation of thefirst data, the communication method comprising: a data transmissionstep of transmitting the first data to the master communication deviceat a random time determined by random numbers set after elapse of afirst time and before elapse of a second time from a time when thecarrier signal on the transmission line is gone in a case where a slavecommunication device of a transmission source transmits the first databy request; a data relay step in which the master communication devicethat has received the first data transmits the first data to a slavecommunication device of a transmission destination before elapse of thefirst time from a time when a carrier signal of the first data on thetransmission line is gone; an ACK transmission step in which the slavecommunication device of the transmission destination transmits ACK datarepresenting a reception confirmation to the master communication deviceafter the reception of the data is confirmed before elapse of the firsttime; and an ACK relay transmission step in which the mastercommunication device that has received the ACK data transmits the ACKdata to the slave communication device of the transmission source beforeelapse of the first time from a time when a carrier signal of the ACKdata on the transmission line is gone.
 4. A communication method inwhich a plurality of communication devices are connected to atransmission line and divided into one master communication device andother slave communication devices to logically form a star-typeconnection and adjust transmission timing of data based on a detectionresult of a carrier signal of another communication device to prevent acollision between signals, thereby performing transmission or receptionof the data via the master communication device, wherein the dataincludes first data whose transmission is requested and ACK datarepresenting a reception confirmation of the first data, thecommunication method comprising: a data transmission step oftransmitting the first data to the master communication device at arandom time determined by random numbers set after elapse of a firsttime and before elapse of a second time from a time when the carriersignal on the transmission line is gone in a case where a slavecommunication device of a transmission source transmits the first databy request; an ACK transmission step in which the master communicationdevice that has received the first data transmits the ACK datarepresenting a reception confirmation to the slave communication deviceof the transmission source after the reception of the first data isconfirmed before elapse of the first time; and a data relay transmissionstep in which the master communication device transmits the first datato a slave communication device of a transmission destination after thetransmission of the ACK data before elapse of the first time from a timewhen a carrier signal of the ACK data is gone.
 5. A communication methodin which a plurality of communication devices are connected to atransmission line and divided into one master communication device andother slave communication devices to logically form a star-typeconnection and adjust transmission timing of data based on a detectionresult of a carrier signal of another communication device to prevent acollision between signals, thereby performing transmission or receptionof the data via the master communication device, wherein the dataincludes multi-address data whose transmission is requested and ACK datarepresenting a reception confirmation of the multi-address data, thecommunication method comprising: a multi-address data transmission stepof transmitting the multi-address data to the master communicationdevice at a random time determined by random numbers set after elapse ofa first time and before elapse of a second time from a time when thecarrier signal on the transmission line is gone in a case where a slavecommunication device of a transmission source transmits themulti-address data by request; an ACK transmission step in which themaster communication device that has received the multi-address datatransmits the ACK data representing a reception confirmation to theslave communication device of the transmission source after thereception of the multi-address data is confirmed before elapse of thefirst time; and a multi-address data relay transmission step ofprocessing a series of data transmissions in which the mastercommunication device transmits the multi-address data to a slavecommunication device of a transmission destination after thetransmission of the ACK data before elapse of the first time from a timewhen a carrier signal of the ACK data is gone and transmits themulti-address data to a slave communication device of a transmissiondestination before elapse of the first time from a time when a carriersignal of the multi-address data is gone.
 6. A communication method inwhich a plurality of communication devices are connected to atransmission line and divided into one master communication device andother slave communication devices to logically form a star-typeconnection and adjust transmission timing of data based on a detectionresult of a carrier signal of another communication device to prevent acollision between signals, thereby performing transmission or receptionof the data via the master communication device, wherein the dataincludes collision avoidance data that is arbitrary data generating acarrier signal on the transmission line and multi-address data whosetransmission is requested, the communication method comprising: acollision avoidance data transmission step of transmitting the collisionavoidance data at a random time determined by random numbers set afterelapse of a first time and before elapse of a second time from a timewhen the carrier signal on the transmission line is gone in a case wherea slave communication device of a transmission source transmits themulti-address data by request; a multi-address data relay transmissionstep in which the slave communication device of the transmission sourcetransmits the multi-address data to the master communication devicebefore elapse of the first time from a time when a carrier signal of thecollision avoidance data is gone; and an multi-address data relaytransmission step of processing a series of data transmissions in whichthe master communication device that has received the multi-address datatransmits the multi-address data to a slave communication device of atransmission destination before elapse of the first time from a timewhen a carrier signal of the multi-address data is gone and transmitsthe multi-address data to a slave communication device of a transmissiondestination before elapse of the first time from a time when the carriersignal of the multi-address data is gone.